New: automatically fix ulimit when possible.

Without this fix, trying to build Cappuccino or run a jake script with a too low `ulimit -n` would cause a fatal error.

This change will automatically increase the ulimit when possible and only error out when it's not. The automatic change does not permanently affect the terminal session as it only targets the soft limit.

narwhal.local.conf

@@ -1,3 +1,11 @@
 if [ -z "$NARWHAL_ENGINE" ] && [ -d "$NARWHAL_HOME/packages/narwhal-jsc" ]; then
 	export NARWHAL_ENGINE=jsc
 fi
+
+if [ "$NARWHAL_ENGINE" == jsc ] && [ `ulimit -n` -lt 1024 ]; then
+    # JSC and Narwhal together open a lot of files. We want to increase the
+    # ulimit to a certain minimum here, but only the soft limit. We avoid
+    # changing the hard limit because someone might want to change the limit
+    # again later.
+    ulimit -Sn 1024
+fi